1. Field of the Invention
The current invention concerns a process for microstructuring surfaces of oriented polymeric substrates using laser radiation. More specifically, the invention involves a process wherein the laser radiation intensity is spatially modulated in a predetermined periodic manner. The process is especially useful for microstructuring the surfaces of textile products.
2. Description of the Related Art
Synthetic melt-spun polymeric fibers, such as polyamide or polyester fibers, typically have smooth surfaces which give rise to undesirable specular reflection. Fabrics prepared from such fibers are perceived by consumers to have a less desirable appearance than fabrics prepared from natural fibers such as cotton or wool. Cotton and wool have irregular, rough surfaces which do not give rise to specular reflections. Also, consumers tend to prefer the tactile aesthetics of natural fibers over those of melt-spun fibers. The preferred tactile aesthetics of these fibers are also believed to be due to their irregular surface which reduces the contact area with the skin.
Bossman & Schollmeyer, U.S. Pat. No. 5,017,423 and Schollmeyer & Bahners, Melliand Textilber. No. 4:251-6 (1990) disclose forming microstructures on the surfaces of synthetic fibers by exposing the fibers to laser radiation. The microstructured surfaces cause the specular reflection to be broken up, resulting in a fiber appearance closely resembling that of natural fibers such as cotton or wool. Generally in such operations, laser radiation in the ultraviolet region is employed due to strong absorption of the photons in this region by the synthetic polymeric fibers. Excimer-type lasers are commonly used to generate such radiation, but these lasers are generally impractical for long-term industrial use because of the costs associated with short electrode life and window fouling.
It is also known that such polymeric substrates have absorption bands in the infrared (IR) region which coincide with wavelengths emitted by known wavelength-tunable lasers, such as CO.sub.2 and CO lasers. However, attempts to use such lasers in accordance with the above-described excimer laser methods in order to microstructure fiber substrates have been unsuccessful. Even as the "fluence" is increased, no microstructuring effect is observed; rather, the fiber eventually melts at a certain fluence level. The term "fluence" denotes the energy in J/cm.sup.2 that is delivered to and absorbed by the fibers when a laser pulse is directed towards them.
The current invention provides a reliable, cost-effective process for microstructuring polymeric surfaces using industrially proven lasers including the CO.sub.2 and CO infrared lasers, special excimer lasers having a large coherence length, and dye lasers. The process of the current invention requires only about one-tenth the fluence (J/cm.sup.2) of that required by conventional methods using standard excimer lasers.